Most of the phenol used in the United States and elsewhere is made by the oxidation of cumene to form cumene hydroperoxide, followed by decomposition or cleavage of the cumene hydroperoxide to produce phenol and yielding acetone as a major coproduct. The first step in the reactor yields cumene hydroperoxide, which decomposes with dilute sulfuric acid or sulfur dioxide to the primary products, plus acetophenone and dimethyl phenyl carbinol. Other processes include sulfonation, chlorination of benzene and oxidation of benzene. The compound is purified by rectification.
Major uses of phenol include production of phenolic resins and para, para-bisphenol A; as a selective solvent for refining lubricating oils; in the manufacture of cyclohexanone, salicylic acid, phenolphthalein, pentachlorophenol, acetophenetidine, picric acid, germicidal paints, and pharmaceuticals; as well as use as a laboratory reagent. Special uses include dyes and indicators, and slimicides.
The conventional phenol process, which dates back to patents to Allied Chemical and Hercules Chemical Co. in the 1950s, is economical as long as there is adequate demand for the acetone coproduct. Because the end uses and rate of growth for phenol and acetone differ, however, with phenol generally experiencing higher growth rates, there has long been a desire to produce phenol without acetone.
In addition, the oxidation of cumene to cumene hydroperoxide (CHP) also results in the formation of some level of dimethylphenyl carbinol (DMPC) also known as dimethylbenzyl alcohol (DMBA). DMPC subsequently dehydrates in the cleavage system to form alpha methylstyrene (AMS) as a significant process byproduct. The AMS then has a known tendency to react with the phenol in the cleavage system to produce cumyl phenol or to dimerize into AMS dimers, both of which are heavier, undesired byproducts, and lead to overall yield loss. Moreover, if an acetone-containing stream is recirculated to an upstream stage, e.g., the cleavage system, the acetone has shown a tendency to form impurities originating from the acetone such as mesityl oxide or hydroxyacetone.
Another problem with the conventional processes for preparing phenol is that the conventional cleavage of cumene hydroperoxide is highly exothermic and requires heat removal to control exotherms, particularly because CHP at higher temperatures can undergo a dangerous thermal decomposition. In conventional processes, cooling can be accomplished by several methods. In one type of cooling scheme the effluent, containing approximately stoichiometric levels of acetone and phenol, as well as lesser amounts of AMS, is cooled and recirculated at the high recirculation ratios (between 20-50:1) that are necessary to control the exotherm. This results, however, in high levels of both AMS and acetone being present under highly reactive conditions, leading to high levels of residues, as well as impurities formed from acetone reactions such as aldol condensations.
Several prior art patents have endeavored to address one or more of the drawbacks, problems, or limitations of conventional phenol processes. U.S. Pat. No. 5,245,090 (DeCaria '090), which is incorporated herein by reference, teaches a two-stage process for producing phenol comprising the steps of decomposing cumene hydroperoxide in a first stage, and subjecting the product of the first stage to hydrogenation in a second stage to convert AMS in the first stage effluent stream to cumene, which is then recycled. The DeCaria '090 patent notes (col. 3, lines 25-32) that the first stage effluent stream must be allowed “sufficient contact time in the second reactor to effect essentially complete decomposition of the residual CHP to phenol and acetone and over 95% disappearance of the DMBA (same as DMPC) and DiCup and to effect virtually complete hydrogenation of AMS . . . to cumene.” Subsequently, DeCaria '090 observes (col. 3, lines 32-26) that this “process can be run . . . with or without the recycle of a portion of the acetone product . . . .” Clearly, therefore, the DeCaria '090 patent does not contemplate the hydrogenation of acetone in the hydrogenation stage. This conclusion is reaffirmed by later portions of the DeCaria '090 patent (e.g., col. 6, lines 12-14). Indeed, claim 1 of DeCaria '090 is specifically directed to a method of making phenol and acetone. Thus, DeCaria '090 does not address the problem of how to transform the acetone coproduct of phenol production into a more useful product or recycle stream or how to reduce formation of undesirable byproducts. Furthermore, a problem with the DeCaria '090 process scheme is the probable poor selectivity of the hydrogenation in the presence of carbonyl compounds. The carbonyl bond in the acetone byproduct can be hydrogenated to form isopropanol. Judged strictly as a byproduct, however, isopropanol is of lesser value than acetone. In fact an appreciable though declining percentage of the acetone in the world is produced from isopropanol as a feedstock.
U.S. Pat. No. 5,015,786 (Araki '786), which is incorporated herein by reference, teaches a process for preparing phenol by the cumene process including the step of converting acetone coproduced with the phenol into isopropanol, thereafter alkylating benzene with the isopropanol and, optionally, with propylene, using a zeolite catalyst to produce cumene, thereby forming phenol without the usual acetone coproduct. Araki '786, however, fails to address the problem of how to handle the AMS component and the other byproduct components of the effluent from the CHP cleavage/decomposition stage.
Somewhat similar to Araki '786 is U.S. Pat. No. 5,017,729 (Fukuhara '729), which is also incorporated herein by reference. Fukuhara '729 teaches a multi-step phenol production process comprising: (a) reacting benzene with propylene to synthesize cumene, (b) oxidizing the cumene of step (a) into cumene hydroperoxide, (c) acid cleaving cumene hydroperoxide into phenol and acetone, (d) hydrogenating the acetone of step (c) into isopropanol, (e) dehydrating the isopropanol of step (d) into propylene, and (f) recycling the propylene of step (e) to step (a). It is also possible to take a propylene product from step (e). The acetone byproduct produced upon preparation of phenol is converted into propylene which Fukuhara '729 teaches is useful by itself for any other uses or which may be recycled to the phenol-producing process. Fukuhara '729 is also similar to the Araki '786 patent in failing to address the problems of handling the AMS and other byproduct components of the effluent from the CHP cleavage/decomposition step.
U.S. Pat. No. 5,160,497 (Juguin '497), which is also incorporated herein by reference, teaches still another variation on a phenol production process addressed specifically to dealing with the less-desired acetone coproduct. Thus, the Juguin '497 patent observes (col. 1, lines 58-61) that: “Nowadays, the main handicap of this [cumene-to-phenol] process lies in the obligatory coproduction of 0.61 ton of acetone per ton of phenol, because the demand for phenol increases much more rapidly than that for acetone.” The improvement of the Juguin '497 patent is stated to be (col. 1, line 66—col. 2, line 2) “in partly or totally hydrogenising the acetone produced into isopropyl alcohol, and in recycling at least partly the latter to the stage of alkylation of benzene where, after dehydration into propene, it will be converted again into cumene.”
The Juguin '497 patent further notes, however, that successful practice of this invention is highly catalyst dependent because (col. 2, lines 8-12) the conventional alkylation catalysts “are not adapted to the reaction of alkylation of benzene in the presence of isopropyl alcohol because they are very sensitive to water . . . .” Instead of using conventional aluminum chloride or phosphoric acid catalysts, Juguin '497 turns to a specific class of zeolite catalyst which had been found to be stable in the presence of the steam generated by dehydration of isopropyl alcohol.
The overall method taught by the Juguin '497 patent is a multi-step process comprising in sequence: an alkylation stage (carried out with at least one catalyst based on a dealuminized Y zeolite having a particular SiO2/Al2O3 molar ratio) to form an effluent stream containing cumene, unreacted benzene, and polyisopropylbenzene; a fractionation step to separate a cumene fraction and a polyisopropylbenzene fraction; a transalkylation stage (again carried out using the particular dealuminized Y zeolite catalyst) where polyisopropylbenzene and benzene are reacted to form additional cumene; a further fractionation step to recover the additional cumene from transalkylation; an oxidation step to oxidize cumene into cumene hydroperoxide; a cleavage step to cleave the cumene hydroperoxide into phenol and acetone; another fractionation step to separate phenol and acetone; and, finally, the step of hydrogenating the acetone into isopropyl alcohol in the presence of a nickel-on-silica catalyst, and recycling the isopropyl alcohol as a feed to the alkylation stage. The Juguin '497 patent does not address how to handle AMS and other byproducts in the effluent from the CHP cleavage stage or how to minimize formation of residue products.
As a result, there remains an unmet need in this art for an integrated cumene-based phenol production method that reduces the formation of undesirable byproducts from AMS and acetone. The aforementioned drawbacks and limitation of the prior art are overcome, in whole or in part, with the methods of this invention for an integrated, efficient, low-residue phenol process which includes hydrogenation of cleavage effluents.